1. Field of the Invention
This invention relates to deformable mirrors in general, and more particularly to deformable mirrors having actuators for deforming the mirrors reflecting surface which may be replaced without requiring disassembly of the entire mirror structure.
2. Summary of the Prior Art
Deformable mirrors are useful for correcting distortions introduced into optical signals by passage of the optical signal through a distorting medium, e.g. the transmission of the optical signal through the Earth's atmosphere. A class of deformable mirrors has been developed with a cooled reflecting surface which permits the use of the deformable mirror for reflecting high energy signals, for example high energy laser signals, or for uses in which the reflecting surface must be cooled to avoid the introduction of thermally-induced distortion into the reflected signal. For a brief introduction into the use of deformable mirrors for controlling optical wavefronts, see the article by J. F. Reintjes appearing the Dec., 1988 issue of Laser Focus/Electro-Optics magazine entitle, ("Nonlinear and Adaptive Techniques Control Laser Wavefronts"). An example of a cooled deformable mirror which may be used for controlling the wavefront of a laser signal is disclosed in U.S. Pat. No. 4,657,358. Deformable mirrors such as that disclosed in the foregoing patent utilize a plurality of actuators, for example piezoelectric actuators, whose length may be independently controlled by the selective application of an electrical signal thereto to selectively deform areas of the mirrors reflecting surface to correct known anomalies contained in an impinging optical signal's wavefront, or to introduce desired distortions into a wavefront.
Cooled deformable mirrors of the type disclosed in the foregoing patent suffer from the defect of having their actuators permanently bonded between the mirror's reflecting facesheet and the base or coolant manifold supporting the facesheet. As in the case of the deformable mirror disclosed in the foregoing patent, the actuators may be used as channels to direct coolant toward and away from the mirror's facesheet, thus also providing the ancillary benefit of cooling the actuator with the circulating coolant, as well as cooling the mirror's facesheet. A deficiency of the foregoing construction, however, is that individual actuators may not be easily removed from the deformable mirror to facilitate replacement of failed or damaged actuators. Consequently, the failure of one or more actuators in the deformable mirror results in a tedious, time-consuming process being required to completely disassemble the deformable mirror to remove the failed actuator and replace it with a new actuator.
U.S. Pat. application Ser. No. 266,616, filed Nov. 3, 1988, now U.S. Pat. No. 4,940,318 discloses a construction for a a deformable mirror having actuators which are threaded into the base of the deformable mirror to permit the actuators to be readily removed from the deformable mirror to facilitate both construction of the mirror and replacement of actuators that fail. However, the foregoing mirror does not provide for cooling of the base manifold, the mirror's faceplate or the actuators. In addition, because the actuators are not directly mechanically fastened to the mirror's facesheet, the deformable mirror must rely on the use of a gradient membrane to retract the facesheet of the deformable mirror to insure mechanical linkage between the actuators and the mirror's reflecting surface. Such a mechanical retraction mechanism can suffer from high cycle fatigue, mechanical hysteresis, and non-linear force response. Consequently, there is a need for an arrangement to permit actuators to be used to channel coolant between a base manifold and a deformable mirror's reflecting facesheet while permitting the actuators to be readily removed from the deformable mirror to facilitate servicing of the deformable mirror. This need is particularly prevalent in deformable mirrors having several hundred actuators, where the laws of probability and statistics dictate that many actuators may ultimately fail, consequently preventing accurate control of the mirror's reflecting facesheet, and therefore rendering as suspect the ability of the deformable mirror to accurately control or introduce distortions into an optical wavefront.